GHSA-77JH-978M-WQHM

Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-05-03 09:33
VLAI?
Details

In the Linux kernel, the following vulnerability has been resolved:

writeback: Fix use after free in inode_switch_wbs_work_fn()

inode_switch_wbs_work_fn() has a loop like:

wb_get(new_wb); while (1) { list = llist_del_all(&new_wb->switch_wbs_ctxs); / Nothing to do? / if (!list) break; ... process the items ... }

Now adding of items to the list looks like:

wb_queue_isw() if (llist_add(&isw->list, &wb->switch_wbs_ctxs)) queue_work(isw_wq, &wb->switch_work);

Because inode_switch_wbs_work_fn() loops when processing isw items, it can happen that wb->switch_work is pending while wb->switch_wbs_ctxs is empty. This is a problem because in that case wb can get freed (no isw items -> no wb reference) while the work is still pending causing use-after-free issues.

We cannot just fix this by cancelling work when freeing wb because that could still trigger problematic 0 -> 1 transitions on wb refcount due to wb_get() in inode_switch_wbs_work_fn(). It could be all handled with more careful code but that seems unnecessarily complex so let's avoid that until it is proven that the looping actually brings practical benefit. Just remove the loop from inode_switch_wbs_work_fn() instead. That way when wb_queue_isw() queues work, we are guaranteed we have added the first item to wb->switch_wbs_ctxs and nobody is going to remove it (and drop the wb reference it holds) until the queued work runs.

Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-31703"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-01T14:16:20Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nwriteback: Fix use after free in inode_switch_wbs_work_fn()\n\ninode_switch_wbs_work_fn() has a loop like:\n\n  wb_get(new_wb);\n  while (1) {\n    list = llist_del_all(\u0026new_wb-\u003eswitch_wbs_ctxs);\n    /* Nothing to do? */\n    if (!list)\n      break;\n    ... process the items ...\n  }\n\nNow adding of items to the list looks like:\n\nwb_queue_isw()\n  if (llist_add(\u0026isw-\u003elist, \u0026wb-\u003eswitch_wbs_ctxs))\n    queue_work(isw_wq, \u0026wb-\u003eswitch_work);\n\nBecause inode_switch_wbs_work_fn() loops when processing isw items, it\ncan happen that wb-\u003eswitch_work is pending while wb-\u003eswitch_wbs_ctxs is\nempty. This is a problem because in that case wb can get freed (no isw\nitems -\u003e no wb reference) while the work is still pending causing\nuse-after-free issues.\n\nWe cannot just fix this by cancelling work when freeing wb because that\ncould still trigger problematic 0 -\u003e 1 transitions on wb refcount due to\nwb_get() in inode_switch_wbs_work_fn(). It could be all handled with\nmore careful code but that seems unnecessarily complex so let\u0027s avoid\nthat until it is proven that the looping actually brings practical\nbenefit. Just remove the loop from inode_switch_wbs_work_fn() instead.\nThat way when wb_queue_isw() queues work, we are guaranteed we have\nadded the first item to wb-\u003eswitch_wbs_ctxs and nobody is going to\nremove it (and drop the wb reference it holds) until the queued work\nruns.",
  "id": "GHSA-77jh-978m-wqhm",
  "modified": "2026-05-03T09:33:09Z",
  "published": "2026-05-01T15:30:32Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31703"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/028103656b84273c73e9e271cf95c9f3421f4b8a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6689f01d6740cf358932b3e97ee968c6099800d9"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9223e5f30403a9b506d6d0bff4f2e29a2d7d46af"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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